The Fusselman Formation is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

in westernmost

Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...

and southern

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

. It preserves

fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

dating back to the early Silurian

period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...

Description

The formation consists mostly of medium to dark gray massive dolomite. It has a light and dark banded appearance due to alternating beds of light gray peritidal laminated

carbonate mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

and dark gray cherty

wackestone Under the Dunham classification (Dunham, 1962Dunham, R.J., 1962. Classification of carbonate rocks according to depositional texture. In: W.E. Ham (Ed.), Classification of Carbonate Rocks. American Association of Petroleum Geologists Memoir. Amer ...

packstone Under the Dunham classification (Dunham, 1962Dunham, R.J. (1962) Classification of carbonate rocks according to depositional texture. In: Classification of Carbonate Rocks (Ed. W.E. Ham), Am. Assoc. Pet. Geol. Mem., 1, 108–121.) system of limesto ...

containing abundant

coral Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...

s. The total thickness is over in the

Florida Mountains The Florida Mountains are a small long, mountain range in New Mexico. The mountains lie in southern Luna County, New Mexico, Luna County about southeast of Deming, New Mexico, Deming, and north of the Chihuahua (state), state of Chihuahua, M ...

but the formation varies greatly in thickness. The formations

unconformably An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval o ...

overlies the

Montoya Group The Montoya Group is a group of geologic formations in westernmost Texas and southern New Mexico. It preserves fossils dating back to the late Ordovician period.Richardson 2008Pope 2004 Description The group consists mostly of dolomitePray 1953 ...

and is overlain by the Onate Formation. The upper contact shows that the area was tilted and eroded prior to the

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

. The formation is divided into the Chamberino, Flag Hill, and Crazycat members in the Sacramento Mountains. Extensive

dolomitization Dolomitization is a geological process where magnesium ions replace calcium ions in the mineral calcite, resulting in the formation of dolomite. Dolomitization conditions are present in Abu Dhabi, the Mediterranean Sea, and some Brazilian hyp ...

of the formation has obscured its primary depositional

fabric Textile is an umbrella term that includes various fiber-based materials, including fibers, yarns, filaments, threads, and different types of fabric. At first, the word "textiles" only referred to woven fabrics. However, weaving is no ...

and made interpretation of its depositional environment difficult.

Fossils

The formation is relatively poor in fossils compared with the underlying

El Paso Formation The El Paso Formation is a geologic formation that is exposed from the Permian Basin of New Mexico and Texas to southeastern Arizona. It preserves fossils dating back to the Ordovician period. Description The formation is composed of gray cher ...

. However, it contains fossils of pentamerid brachiopods, corals, and

stromatoporoid Stromatoporoidea is an extinct clade of sea sponges common in the fossil record from the Middle Ordovician to the Late Devonian.Stock, C.W. 2001, Stromatoporoidea, 1926–2000: ''Journal of Paleontology'', v. 75, p. 1079–1089. They can be cha ...

s. These include the corals ''Cyanthophyllum'', ''

Favosites ''Favosites'' is an extinct genus of tabulate coral characterized by polygonal closely packed corallites (giving it the common name "honeycomb coral"). The walls between corallites are pierced by pores known as mural pores which allowed transfe ...

'', ''

Halysites ''Halysites'' (meaning ''chain coral'') is an extinct genus of tabulate coral. Colonies range from less than one to tens of centimeters in diameter, and they fed upon plankton. These tabulate corals lived from the Ordovician to the Devonian (f ...

'', and ''

Heliolites ''Heliolites'' is a large and heterogenous genus of extinct tabulate corals in the family Heliolitidae. Specimens have been found in Ordovician to Devonian beds in North America, Europe, Africa, Asia, and Australia. The genus is particularly ab ...

'' and the

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

''Hormatoma''.

Economic geology

The uppermost part of the formation shows significant

barite Baryte, barite or barytes ( or ) is a mineral consisting of barium sulfate (Ba S O4). Baryte is generally white or colorless, and is the main source of the element barium. The ''baryte group'' consists of baryte, celestine (strontium sulfate), ...

fluorite Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. The Mohs scal ...

and

base metal A base metal is a common and inexpensive metal, as opposed to a precious metal such as gold or silver. In numismatics, coins often derived their value from the precious metal content; however, base metals have also been used in coins in the past ...

mineralization, where migrating fluids are trapped by the overlying impermeable

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

formations.

History of investigation

The name was first used by G.B. Richardson in 1908 for outcrops in Fusselman Canyon in the Franklin Mountains. It was divided into members in the Florida Mountains by Kottlowski and Pray in 1967.

Footnotes

References